Steel strut aluminum piston



May 16, 1933.

R. E. RASMUSSEN STEEL STRUT ALUMINUM PISTON 'Filed Feb. '7,- 19:51

Patented May 16, 1933 UNITED STATES I l p 1,909,633

RIGHABD E. RASMUSSEN, F DETROIT, MICHIGAN STEEL STRUT ALUMINUM PISTON-Applioation led February 7, 1981. Serial No. 514,193.

My invention relates to cast metal pistons for internal combustionengines of the type wherein two struts extending transverse to the axisof the piston pin are placed inthe mould and embedded in the metal ofthe' chosen so as to cause the diameter to increase at substantially thesame rate as the diameter ofthe cylinder in which the piston operatesincreases as the engine becomes heated.

Such pistons are commonly made of aluminum or of an alloy of whichaluminum forms the principal ingredient, and inasmuch as aluminumexpands faster than castV iron, the material from which the cylinder ofthe engine is made, the piston if it fits properly when the engineiscold will tend to `score the cylinder wall and seize therein as theparts become heated; and on the other hand if such a piston is madesmall enough in diameter so as not to bind when the engine is hot itwill be so loose in the cylinder as to be noisy, the phenomena of pistonslap, when the engine is being started from a cold condition. Thescoring or seizing being a fault particu 30 larly to be avoided theresult is that aluminum pistons are commonly made smaller in diametereven than is necessary for proper running at high temperatures,

with the result that such pistons are ordinarily more noisy than castiron pistons.

As herein first appears, such pistons have heretofore been provided withtransverse struts which expand not at all, or at a rate much less'thanthat of aluminum, in order 40 to maintain, as nearlyv as possible, aconstant diameter of piston as the engine becomes heated; or a diameterwhich increases at approximately the same rate that the diameterY lofthe cast iron cylinder of the engine increases. In such pistons,however, no provision has commonly been made for controlling thediameter of the bearings for the piston pin and, inasmuch as it ishighly desirable that the bearing surface for the pin shall be of thesame aluminum or equivalent metal as that from which the piston is cast,the fit ofthe steel piston pin in the aluminum bearings therefor hasVaried with the temperature; being tighter when the engine is cold andlooser, because of the more rapid expansion of the aluminum bearingsthan the expansion of the steel pin, when the parts have become heated;the result'being that such looseness as is necessary to permit theassembling of the parts and operation without binding orscoring at lowtemperatures, will increase to an objectionable degree as the enginebecomes hot.

The object of my invention therefore is to provide a piston wherein andin addition to the controlling of the external diameter thereof thediameter of the bearings for the piston pin will also be controlled,thus providing a piston wherein the clearance between the pin and itsbearings as well as the clearance between the piston and the cylinderwill be constant or substantially so at all temperatures. The preferredform of my invention is illustrated in the drawing `accompanying andforming a part of this specification; although the same may be embodiedin other forms, and my invention includes such other A forms as comewithin the scope of the claims at the end of this description.

In the drawing: x

Figure 1 is a view showing a piston made in accordance with myinvention, in elevatlon.

Figure 2 is a view partly in section upon a central vertical planeextending along the 85 axis of the piston pin bearings, as indicated bythe line 2 2, Figure 1, and partly in elevation as seen from a positionto the right of Figure 1.

Figure 3 is a view showing a section upon ,90

a plane at right angles to the axis of the piston and located at theaxis of the piston pin bearings.

Figure 4y is a view showing the strut member of my improved piston inperspective, with its part separated.

Figure 5 is a view similar to Figure 1 but showing certain pistonfeatures not shown in Figures 1 to 3.

Figure 6 1s a vlew showing a section upon 10 l an inclined planeindicated-by the line 6-6,

liti:

Figure 5.

Referring now to the drawing and to the particular embodiment of myinvention which it illustrates, the reference numeral 10 designates thehead portion of the piston; and below the head and extending downwardlytherefrom to form a guide or skirt portion are oppositely arrangedslippers 11 which are ordinarily separated from the head by slots l2, soas to permit the head to expand without carrying the upper end of theskirt along with it. The lower ends of the slippers are ordinarilyconnected by arcuate connecting parts 13 to provide a complete ring atthe lower end of the skirt or guiding part of the piston; although myinvention, so far as it concerns the controlling of the expansion forthe bearings for the piston pin, is equally useful in pistons not havingthe slots 12, and in which the slippers extend so as to form a completecylindrical skirt portion for guiding the piston within the cylinder inwhich it operates.

Arranged below the head are piston pin bosses 14 for the two ends of apiston pin, not shown. rllhese bosses are shown as supported from thehead by depending supports or piers 15. ln the form of my inventionillustrated in Figures l'to 3 there is no connection formed by thecast-metal of the piston between the pin bosses and the skirt portionmade up of the slippers 11 and lower connections 13, while in the formillustrated in Figures 5 and 6 there are connections 16 of cast metalbetween the pin bosses and the slippers which connect the head andbosses y, vand the skirt together and form an integral structure as thepiston is cast.

rllhe parts thus far described are made from cast metal, commonlyaluminum or aluminum alloy as explained, by the use of a suitable mould.As a matter of course the' periphery of the casting thus produced is.properly finished to provide a cylindrical tend from above the pinbosses downward and below the pin bosses.v These struts are placed inthe mould and when the moulten metal is poured thereinto their centralparts become embedded in the pin bosses, and their extremities in theslippers, in substantially the way shown in Figures 2 and 3.

Lacasse rlllhe metal of the struts must obviously be one which will notbe melted by the fluid metal which forms the piston as it enters themould and flows into contact with them. Steel is a good material for thestruts, and

a steel may be chosen having a composition such that it expands verylittle with change in temperature; so that as the piston becomes heatedin use its diameter will increase but slightly and at a rate not greaterthan the rate of expansion of the cast iron cylinder in which the pistonoperates. llnvar is also a suitable materia-l, although more expensive,and when an invar strut` is used a substantially constant diameter ofpiston at all temperatures is maintained because invar expands to but anegligible extent when it is heated.v rIhe struts therefore control thediameter of -the skirt as it can increase in diameter only to the extentthat the struts expand and increase in length. This is so in the Figure5 form no less than in the Figure 1 form because in the former the ties16 in contracting place the struts under compression which is notrelieved when the piston becomes hot in use, as it never attains atemperature even remotely approaching that of the piston metal when itlsolidiies and commences to compress the struts and to set up contractilestresses in the ties 16.

Associated with the struts 17 and embedded in the piston pin bosses 14are rings the purpose of which is to control the diameter of thebearings in the bosses for the ends of the piston pin. These rings maybe variously provided, and variously arranged except that they must belarger in internal diameter than the diameter of the piston pinbearings, so that the bearing surfaces for the pin are always of thesame metal as that from which the piston is cast. The rings arepreferably integral with or fastened to the struts in order to provide aplan for conveniently and effectively supporting them inside the mouldin such positions that they will be embedded in the bosses, asexplained, although insofar as their function of controlling thediameter of the piston pin bearings is concerned theyneed not befastened to the struts.

lln the form of my invention illustrated each struct has tworings,"although the two forme-in eect but a single ring. That is eachstrut has a Hange or ring 18 formed by Hanging the material of thestrut, as shown, and which Harige extends substantially parallel withthe piston pin bearing; and is provided with holes 19 through which thefluid metal runs during the casting of the pis ton. lln addition eachstrut is preferably provided with a second ring 20 having a base 21fastened to the strut asby welding, and which second ring i-sV providedwith holes 22 like and for the same purpose as the holes 19. The tworings are larger `)than the piston pin bearing to an extent suiiicientto provide a bearing surface inside the rings of the same metal as themetal from which the piston is cast, as appears in Figures 2 and 3.

The metal of the rings is of the same character as that of the struts,from which it follows that the diameter of the bearings for the two endsof the piston pin is controlled by the rings; and said rings, inaddition to controlling the diameter of said bearings, provides a moresecure anchoring of the struts in the piston pin bosses, as will beappreciated.

Having'thus described and explained my invention I claim and desire tosecure by Letters Patent:

1. In a cast metal piston of the class described, a rectangular strutembedded in the piston during the casting thereof and extendingtransverse to the axis of a piston pin bearing between parts of thepiston which are spaced apart from one another, and which strut has aring upon each side thereof, which rings extend substantially parallelwith said bearing and the diameters of which are materially greater thanthe diameter of said bearing; so that metal from which the piston ismade will embed said rings during the casting of the piston and form abearing of said metal inside the rings for the piston pin and wherebyexpansion of the bearing as the piston becomes heated will be controlledby said rings; said rings together being of a length corresponding,approximately, with the length of the bearing in which they areembedded.

2. In a cast metal piston of the class described, a rectangular strutembedded in the piston during the casting thereof and extendingtransverse to the axis of a piston pin bearing between parts of thepiston which are spaced apart from one another, and which strut has twooppositely disposed rings one formed integrally therewith and the otherformed separately and secured thereto, and which rings are substantiallyparallel with the axis of saidbearing and materially larger than saidbearing, and have holes in their walls; so that metal from which thepiston is formed will embed said ring during the cast ing of the pistonand form a bearing for the piston pin of said metal inside the ring, andwhereby expansion of the bearing as the piston becomes heated will becontrolled by said rings; said rings together being of a lengthcorresponding, approximately, with the length of the bearing in whichthey are embedded.

In testimony whereof I aix my signature.

RICHARD E. RASMUSSEN.

